The statements in this section may serve as a background to help understand the invention and its application and uses, but may not constitute prior art.
Hip replacement surgery such as total hip arthroplasty (total hip replacement, THR) and hemiarthroplasty is a surgical procedure commonly used to relieve pain, restore function, and improve the quality of life for patients with compromised hip joints when conservative treatments have failed. Despite its success, hip replacement surgery may also lead to complications such as aseptic loosening, stress shielding, and even periprosthetic fracture. Bone resorption secondary to stress shielding can also arise from the mismatch of the mechanical properties between the implant and the surrounding native femoral bone.
Although hip replacement implants have been used and greatly improved in their form and construction over the years, several issues still exist for conventional hip implant designs. First, conventional hip implants are prefabricated with several standard, fixed sizes. Doctors choose a best fitting implant according to patient's personal bone size and conditions. For example, the diameter of the femoral head and the size of the femoral stem are often estimated with preoperative planning, and further manually confirmed and fitted intraoperatively by testing the femoral head prosthesis within the acetabulum, and the femoral stem within the medullary canal based on cement usage. However, each person is different with unique bone anatomies, so very often a standard size does not match the patient's bone perfectly as desired. A poor fit reduces the longevity of device, leading to device failures and harmful wear particles.
Second, existing hip implants are mostly made through casting and molding processes with solid metals such as chromium-cobalt alloy, the density of which is more than twice as that of natural bone. A heavier implant can cause discomfort and a reduced quality of life for the patient.
Third, current implant materials such as titanium-based alloys, chromium cobalt alloys, and 316L stainless steel have stiffness significantly higher than that of natural bone. Once a metal implant is secured in place, most of the physiological loading is transferred to the implant, with stress “shielded” away from the surrounding femur. As healthy bones constantly remodel in response to the load they are placed under, the load transfer in the implanted femur causes under-loading of the bone, leading to bone resorption and loss of bone mass. This phenomenon is termed as bone loss secondary to stress shielding. The reduction in bone stock can lead to serious complications, including peri-prosthetic fracture, while the mismatch in elastic modulus between the implant and the bone can result in thigh pain. Stress shielding also obstructs bone growth and reduces the quality of the remaining bone stock, leading to a significantly increased risk of fracture and aseptic loosening with revision surgery.
Therefore, in view of the aforementioned difficulties, there is an unsolved need for personalized hip implants and implant components with optimal weight and stiffness for faster bone growth, bone density matching, and enhanced fatigue strength.
It is against this background that various embodiments of the present invention were developed.